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[PATCH] iio: stm32: fix adc/trigger link error

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  [PATCH] iio: stm32: fix adc/trigger link error Arnd Bergmann <arnd@arndb.de> - 2017-09-06 15:00 +0200
    Re: [PATCH] iio: stm32: fix adc/trigger link error Fabrice Gasnier <fabrice.gasnier@st.com> - 2017-09-06 18:20 +0200

#1727430 — [PATCH] iio: stm32: fix adc/trigger link error

The ADC driver can trigger on either the timer or the lptim
trigger, but it only uses a Kconfig 'select' statement
to ensure that the first of the two is present. When the lptim
trigger is enabled as a loadable module, and the adc driver
is built-in, we now get a link error:

drivers/iio/adc/stm32-adc.o: In function `stm32_adc_get_trig_extsel':
stm32-adc.c:(.text+0x4e0): undefined reference to `is_stm32_lptim_trigger'

We could use a second 'select' statement and always have both
trigger drivers enabled when the adc driver is, but it seems that
the lptimer trigger was intentionally left optional, so it seems
better to keep it that way.

This adds a hack to use 'IS_REACHABLE()' rather than 'IS_ENABLED()',
which avoids the link error, but instead leads to the lptimer trigger
not being used in the broken configuration. I've added a runtime
warning for this case to help users figure out what they did wrong
if this should ever be done by accident.

Fixes: f0b638a7f6db ("iio: adc: stm32: add support for lptimer triggers")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/linux/iio/timer/stm32-lptim-trigger.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/iio/timer/stm32-lptim-trigger.h b/include/linux/iio/timer/stm32-lptim-trigger.h
index 34d59bfdce2d..464458d20b16 100644
--- a/include/linux/iio/timer/stm32-lptim-trigger.h
+++ b/include/linux/iio/timer/stm32-lptim-trigger.h
@@ -16,11 +16,14 @@
 #define LPTIM2_OUT	"lptim2_out"
 #define LPTIM3_OUT	"lptim3_out"
 
-#if IS_ENABLED(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
+#if IS_REACHABLE(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
 bool is_stm32_lptim_trigger(struct iio_trigger *trig);
 #else
 static inline bool is_stm32_lptim_trigger(struct iio_trigger *trig)
 {
+#if IS_ENABLED(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
+	pr_warn_once("stm32 lptim_trigger not linked in\n");
+#endif
 	return false;
 }
 #endif
-- 
2.9.0

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#1727631

On 09/06/2017 02:56 PM, Arnd Bergmann wrote:
> The ADC driver can trigger on either the timer or the lptim
> trigger, but it only uses a Kconfig 'select' statement
> to ensure that the first of the two is present. When the lptim
> trigger is enabled as a loadable module, and the adc driver
> is built-in, we now get a link error:
> 
> drivers/iio/adc/stm32-adc.o: In function `stm32_adc_get_trig_extsel':
> stm32-adc.c:(.text+0x4e0): undefined reference to `is_stm32_lptim_trigger'
> 
> We could use a second 'select' statement and always have both
> trigger drivers enabled when the adc driver is, but it seems that
> the lptimer trigger was intentionally left optional, so it seems
> better to keep it that way.
Hi Arnd,

This is correct, not all stm32 have this hardware.
> 
> This adds a hack to use 'IS_REACHABLE()' rather than 'IS_ENABLED()',
> which avoids the link error, but instead leads to the lptimer trigger
> not being used in the broken configuration. I've added a runtime
> warning for this case to help users figure out what they did wrong
> if this should ever be done by accident.
> 
> Fixes: f0b638a7f6db ("iio: adc: stm32: add support for lptimer triggers")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Fabrice Gasnier <fabrice.gasnier@st.com>

Many thanks for the fix,
Best Regards,
Fabrice
> ---
>  include/linux/iio/timer/stm32-lptim-trigger.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/iio/timer/stm32-lptim-trigger.h b/include/linux/iio/timer/stm32-lptim-trigger.h
> index 34d59bfdce2d..464458d20b16 100644
> --- a/include/linux/iio/timer/stm32-lptim-trigger.h
> +++ b/include/linux/iio/timer/stm32-lptim-trigger.h
> @@ -16,11 +16,14 @@
>  #define LPTIM2_OUT	"lptim2_out"
>  #define LPTIM3_OUT	"lptim3_out"
>  
> -#if IS_ENABLED(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
> +#if IS_REACHABLE(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
>  bool is_stm32_lptim_trigger(struct iio_trigger *trig);
>  #else
>  static inline bool is_stm32_lptim_trigger(struct iio_trigger *trig)
>  {
> +#if IS_ENABLED(CONFIG_IIO_STM32_LPTIMER_TRIGGER)
> +	pr_warn_once("stm32 lptim_trigger not linked in\n");
> +#endif
>  	return false;
>  }
>  #endif
> 

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